“JUNGLE”: The mud below

If the movies have taught us anything it is that when privileged young people go carousing in the wilderness, bad shit happens.

“Jungle,” based on Yossi Ginsberg’s 2005 memoir, is jam packed with bad shit.

This grueling tale of survival finds Daniel Radcliffe once again going out on a limb (and distancing himself from his “Harry Potter” heritage) as Yossi, who has fled his native Israel and grownup responsibilities for a year or so of backpacking around the globe.

Directed by Aussie auteur Greg McLean, best known for brutally violent horror films like “Wolf Creek” and “Rogue,” this real-life misadventure unfolds in Bolivia.

There Yossi (Radcliffe) falls in with a couple of fellow free spirits, the young American photographer Kevin Gayle (Alex Russell) and Marcus (Joel Jackson), a Swiss fellow described as having “the heart of a poet and the soul of a saint.” These, of course, are qualities of absolutely no use in a South American rain forest.

Out of nowhere they are approached by Karl (Thomas Kretschnmann), an Austrian geologist who claims to know the jungle like the back of his hand. He has tales of lost Indian tribes and rivers peppered with gold nuggets. His semi-mystical rap is so convincing our trio agree to accompany Karl on a hike into the unknown.

Given that this takes place in 1981, well before cell phones, GPS or the Internet, it’s a given that when things go bad — and they soon do — there will be no easy way out.

There’s a sort of Lord of the Flies element at work here. Lovable Marcus is spooked by the jungle and soon suffers crippling physical distress. He’s slowing the progress of the other hikers, who hope to complete their trek before the arrival of the rainy season. Tempers flare. Things get nasty.

And then there’s Karl, who gleefully introduces the boys to the delights of monkey meat but seems curiously unschooled in other aspects of wilderness survival. He may not be able to swim, a real drawback once the decision is made to build a raft on which to float downstream.

The second hour of “Jungle” is virtually a one-man show as Yossi, separated from his fellows, sets out on a desperate march of survival.

He eats snake and half-formed birds straight from the egg, endures downpours and mudslides, quicksand and a stalking jaguar. Toward the end he’s beset by hallucinations, including an Indian woman (Yasmin Kassim) who briefly serves as Friday to his Robinson Crusoe.

The trials Yossi goes through are depicted in alarming detail, the most grotesque being a sequence in which Yossi plucks a long worm-like parasite out of an infected cyst on his forehead. Yuk.